High early strength pozzolan cement blends

ABSTRACT

A high early strength pozzolan cement includes larger sized pozzolan particles blended with smaller sized hydraulic cement particles containing tricalcium silicate and/or dicalcium silicate (e.g., Portland cement). Excess calcium release from the hydraulic cement when mixed with water forms calcium hydroxide available for reaction with the pozzolan. The fineness of the hydraulic cement particles is substantially greater than the fineness of the pozzolan particles (e.g., about 1.25 to about 50 times greater). Reducing or eliminating coarse hydraulic cement particles that cannot fully hydrate but include unreacted cores reduces or eliminates wasted cement normally found in concrete. Replacing some or all of the coarse cement particles with pozzolan particles provides a pozzolan cement composition having significantly lower water demand compared to the hydraulic cement by itself.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of co-pending U.S. patent applicationSer. No. 12/576,117, filed Oct. 8, 2009, which claims the benefit ofU.S. Provisional Application No. 61/104,661, filed Oct. 10, 2008. Thedisclosures of the foregoing applications are incorporated herein intheir entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is generally in the field of hydraulic cement used in themanufacture of concrete, more particularly to hydraulic cements thatinclude pozzolans.

2. Relevant Technology

“Roman cement” was used by the Romans to build spectacular buildings andaqueducts that still stand after 2000 years. Roman cement was formed bymixing a pozzolan (e.g., volcanic ash or ground brick) with lime andwater to form a lime-pozzolan cement. The hydration products of Romancement are essentially the same as in modern Portland cement but theyform much more slowly, making Roman cement impractical as a moderncementing material.

In modern concrete, pozzolans such as fly ash and volcanic ash are oftenused to replace a portion of Portland cement. Replacing a portion ofPortland cement with pozzolan yields improved concrete with higherdurability, lower chloride permeability, reduced creep, increasedresistance to chemical attack, lower cost and reduced environmentalimpact. Pozzolans react with excess calcium hydroxide released duringhydration of Portland cement and therefore help prevent carbonation.However, there is a limit to how much Portland cement can be replacedwith pozzolan because pozzolans generally retard strength development.

Notwithstanding the potential economic and environmental benefits thatwould derive from increasing the pozzolan content and reducing thePortland cement content when manufacturing concrete, technical limitshave limited their practical use to current levels. It is estimated thatless than 40% of ready mix concrete in the United States uses anypozzolan at all and of those that do use pozzolans, the typicalreplacement level is about 10%-15%. While highly engineered concretescan include more pozzolan as a percentage of total binder, engineeringconcrete to overcome the deficiencies of blended cements comes at a highcost that is usually only justified in expensive building projects suchas high rise buildings and large public works structures where thebeneficial properties of the pozzolan outweigh the engineering costs. Inmost cases, the tendency of pozzolans to retard concrete strengthdevelopment creates an upper replacement limit beyond which theadvantages of Portland cement replacement disappear. In short, when costand ease of manufacture are the chief concerns, such as in the case ofgeneral purpose concretes, pozzolans are typically used in low amountsor not all.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to pozzolan cement blends that areparticle size optimized to increase the level of pozzolan replacement ofPortland cement while maintaining high early strength development. Byincreasing pozzolan replacement levels without significantly reducingearly strength development, the inventive pozzolan cement blends morefully realize the economic and environmental benefits of pozzolanreplacement compared to existing cements and concretes.

According to one embodiment, pozzolan cement blends are provided thatcan be readily substituted for ordinary Portland cement (OPC) (e.g.,Type I and II cements). The inventive pozzolan cement blends avoid thestrength retarding effects of pozzolan by maintaining the same orsimilar concentration of highly reactive fine Portland cement particles(e.g., a distribution of about 0.1-10 μm) found in ordinary Portlandcement (OPC). The coarse Portland cement particles are replaced with asimilar quantity of coarse pozzolan particles having the same or similarparticle size distribution and/or fineness. The coarse pozzolanparticles help disperse and moderate the reaction of the fine Portlandcement particles, reduce water demand, and provide long-term strengthdevelopment in much the same way as the coarse Portland cement particlescontained in OPC.

Both OPC and fly ash typically have a particle size distribution rangingfrom about 0.1-45 μm, with about half the volume consisting of “fine”particles below about 10-15 μm and half consisting of “coarse” particleslarger than about 10-15 μm. An optimized blend of Portland cement andfly ash or other pozzolan can be provided by (1) removing the coarseparticles from Portland cement and keeping mainly or exclusively thefine particles, (2) removing some or all of the fine particles from thepozzolan and keeping the coarse particles, and (3) blending the finePortland cement and coarse pozzolan particles together. The result is anew pozzolan cement blend that provides the same or similar earlystrength development in concrete as OPC. And it costs substantially lessthan OPC.

According to one embodiment, there can be a cutoff particle sizeseparating the Portland cement and pozzolan particles (e.g., rangingfrom about 5-30 μm). In this embodiment, most or all of the Portlandcement particles will be at or below the cutoff size (e.g. less thanabout 20 μm, 15 μm, 10 μm, 7.5 μm, or 5 μm), and most or all of thepozzolan particles will be at or above the cutoff size (e.g., greaterthan about 5 μm, 7.5 μm, 10 μm, 15 μm, or 20 μm). In some cases, thelevel of pozzolan replacement of Portland cement can be adjusted bychanging the particle size cutoff. Raising the particle size cutoffgenerally decreases the level of pozzolan replacement and lowering thecutoff increases the level of pozzolan replacement. In some embodiments,there can be significant overlap between the Portland cement andpozzolan particle sizes so long as the overall fineness of the Portlandcement fraction substantially exceeds the fineness of the pozzolanfraction. A relatively small quantity of fine pozzolan particles may beincluded to help disperse the fine Portland cement particles.

In contrast to existing methods for increasing the reactivity and earlystrength development of pozzolan cement blends, which generally involvethe use of finer pozzolans, whether by grinding or selection, thepozzolanic cements disclosed herein are made using the counterintuitiveapproach of maintaining a relatively coarse pozzolan fraction or evendecreasing the fineness of the pozzolan fraction. In general, theinvention provides high early strength pozzolan cement by shifting thebalance of particle size distribution in the cement composition towardpredominantly larger-sized pozzolan particles and smaller-sizedhydraulic cement particles. In this way, the hydraulic cement andpozzolan fractions are put to their highest respective uses.

It has been found that it is primarily the smaller cement particles thatprovide early strength development of OPC. Due to slow and limitedpenetration of water into cement grains during hydration, only the verysmall Portland cement particles (e.g., 0.1-5 μm) are fully hydrated inthe first 28 days. Larger particles are only partially hydrated at thesurface. Portland cement particles larger than 10-20 μm can take yearsto fully hydrate. The use of larger-sized Portland cement particles iswasteful because the unreacted inner volumes of such particles act asexpensive fillers during the relevant strength development period.Nevertheless, the inclusion of larger sized Portland cement particles inOPC is necessary to regulate set time, provide desired water demand andrheology, and contribute to long term strength. Very finely groundPortland cement falls within Type III rapid hardening cement, whichdevelops higher early strength but lower long-term strength than Types Iand II cement.

In order to maintain a similar strength development profile as OPC andmaintain similar water demand and rheology, most or all of the largersized hydraulic (e.g., Portland) cement particles can be replaced withsimilarly sized pozzolan particles. In the short term, the slow reactingpozzolan particles behave similarly to the larger sized hydraulic cementparticles they replace. They react enough and are sufficientlychemically compatible with the small, hydrating cement particles thathigh early strength is maintained. However, unlike unreactive fillers,such as ground inert stone or sand, pozzolans continue to react andcontribute to the growth of cement paste and concrete strength overtime. Because pozzolan cements can, in the long term, develop strengthsthat equal or exceed that of OPC, the long term strength of theinventive pozzolan cements can also equal or exceed that of OPC.

The ability to replace moderate to high levels of the Portland cementwith a pozzolan and maintain similar strength and performancecharacteristics as OPC is a surprising and unexpected result madepossible by keeping the particle size distribution of the overallpozzolan cement blend similar to OPC while using smaller Portland cementparticles. As compared to a traditional blend of OPC and pozzolan, thepozzolan cement blends have a higher percentage of small Portland cementparticles that fully hydrate in 28 days, thereby unleashing all of thepotential of the Portland cement in the desired time frame. Thisincreased utilization of the Portland cement is one principle reasonthat the pozzolan cement blends described herein can achieve similarperformance characteristics as OPC with high volumes of pozzolan.

The finer Portland cement particles also benefit the coarse pozzolanfraction. The fully hydrated fine Portland cement particles releaseadditional lime, which accelerates the pozzolanic reaction and producesincreased long term strength. Thus, the combination of fine cementparticles and coarse pozzolan particles creates a synergy that cannot beachieved by blending the full range particle distributions of pozzolansand Portland cement as is currently practiced.

Another significant benefit of particle size optimized pozzolan cementblends is the reduction in carbon dioxide emissions. It is estimatedthat Portland cement contributes 5% or more of man-made carbon dioxide.The wasted cement in the core of unhydrated cement particles representsa wasted environmental cost that is mitigated in the pozzolan cementblends described herein. This reduction in the use of cement representsa true reduction in carbon emissions because it comes at no loss to theperformance of the cement.

In some cases it may be desirable supplement the amount of excesscalcium hydroxide provided by the hydraulic cement by adding calciumoxide or calcium hydroxide. Lye or other strong bases can also be addedto accelerate the lime-pozzolan reaction. Alternatively, the relativeamount of calcium in the hydraulic cement fraction can be increased byincreasing the ratio of tricalcium silicate to dicalcium silicate in thecement clinker.

In short, by properly balancing the relative quantities and particlesize distributions of the larger pozzolan particles and smallerhydraulic cement particles, the present invention provides pozzolancement compositions that can have the same or better early and ultimatestrength compared to OPC, while exhibiting similar or superior flowproperties, durability, reduced permeability and resistance to chemicalattack. And it can do so at lower cost, reduced CO₂ emissions, and whilereducing or eliminating the use of expensive admixtures compared tocurrent schemes that overload or replace OPC with finely groundpozzolans to provide higher early strength and long term strength anddurability.

These and other advantages and features of the present invention willbecome more fully apparent from the following description and appendedclaims, or may be learned by the practice of the invention as set forthhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent invention, a more particular description of the invention willbe rendered by reference to specific embodiments thereof which areillustrated in the appended drawings. It is appreciated that thesedrawings depict only illustrated embodiments of the invention and aretherefore not to be considered limiting of its scope. The invention willbe described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIG. 1 is a schematic of a system for producing a pozzolan cement blend;and

FIG. 2 is a graph comparing a pozzolan cement blend with control blendsand 100% Portland cement.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS I. Introduction

Disclosed herein is a high early strength pozzolan cement that can takethe place of ordinary Portland cement (e.g., Type I and II cements) usedin both common and high end construction. The inventive pozzolan cementsinclude a unique distribution of pozzolan and hydraulic cement particlesin which the larger sized particles comprise mostly or exclusivelypozzolan and the smaller sized particles comprise mostly or exclusivelyhydraulic cement. The calcium hydroxide required to effect hydration ofthe pozzolan is provided by excess calcium from the hydraulic cementfraction. The result is a cement composition that provides high earlystrength similar to OPC with superior long-term strength and durability,and lower cost and CO₂ output.

Rather than wasting Portland cement in the form of large particles thatonly react on the surface and which mainly act as expensive fillers, theinvention unlocks much more of the binding ability of the hydrauliccement by utilizing finer, more reactive particles that becomesubstantially or fully hydrated in the short term (e.g., 7 days, 28 daysor 45 days). Rapid hardening of the finer hydraulic cement particles iscontrolled and water demand is reduced by utilizing larger pozzolanparticles that help disperse the hydraulic cement particles. In thisway, the hydraulic cement and pozzolan fractions are put their highestrespective uses.

According to one embodiment, a high early strength pozzolan cement canbe made which has a Blaine fineness and particle size distribution(e.g., as described by the Rosin-Rammler-Sperling-Bennet distribution)that approximates that of OPC. In this way, the cement composition canbehave similar to OPC in terms of water demand, rheology and strengthdevelopment.

Except as otherwise specified, percentages are to be understood in termsof weight percent. It will be appreciated, however, that where there isa significant disparity between the density of the hydraulic cement andthat of the pozzolan, adjustments can be made so that an equivalentvolume of pozzolan is added in place of a similar volume of hydrauliccement being replaced. For example, the correct weight of pozzolanreplacement may be determined by multiplying the weight of cementreduction by the ratio of the pozzolan density to the cement density.

II. Cement Compositions

A. Particle Size Distributions

The particle size of perfectly spherical particles is measured by thediameter. While fly ash is generally spherical owing to how it isformed, Portland cement and pozzolan particles may be non spherical.Thus, the “particle size” shall be determined according to acceptedmethods for determining the particle size of ground or other otherwisenon spherical materials, such as Portland cement and many pozzolans. Thesize of particles in a sample can be measured by visual estimation or bythe use of a set of sieves. Particle size can be measured individuallyby optical or electron microscope analysis. The particle sizedistribution (PSD) can also be determined or estimated by laser or x-raydiffraction (XRD).

The pozzolan cement compositions (i.e., blended cements) according tothe invention typically include a distribution of particles spreadacross a wide range of particle sizes (e.g., over a range of about0.1-120 μm, or about 0.1-100 μm, or about 0.1-80 μm, or about 0.1-60 μm,or about 0.1-45 μm). According to one embodiment, at least 50% of thecombined pozzolan and hydraulic cement particles larger than about 20 μm(e.g., distributed over a range of about 20-100 μm, or about 20-60 μm)comprise pozzolan and less than 50% comprise hydraulic cement.Preferably, at least about 65% of the particles larger than about 20 μmcomprise pozzolan and less than about 35% comprise hydraulic cement.More preferably, at least about 75% of the particles larger than about20 μm comprise pozzolan and less than about 25% comprise hydrauliccement. Even more preferably, at least about 85% of the particles largerthan about 20 μm comprise pozzolan and less than about 15% comprisehydraulic cement. Most preferably, at least about 95% of the particleslarger than about 20 μm comprise pozzolan and less than about 5%comprise hydraulic cement. In some cases it may be desirable foressentially all of the particles larger than about 20 μm to comprisepozzolan and none to comprise hydraulic cement.

In another embodiment, at least 50% of the combined pozzolan andhydraulic cement particles larger than about 15 μm (e.g., distributedover a range of about 15-100 μm, or about 15-60 μm) comprise pozzolanand less than 50% comprise hydraulic cement. Preferably, at least about65% of the particles larger than about 15 μm comprise pozzolan and lessthan about 35% comprise hydraulic cement. More preferably, at leastabout 75% of the particles larger than about 15 μm to comprise pozzolanand less than about 25% comprise hydraulic cement. Even more preferably,at least about 85% of the particles larger than about 15 μm comprisepozzolan and less than about 15% comprise hydraulic cement. Mostpreferably, at least about 95% of the particles larger than about 15 μmcomprise pozzolan and less than about 5% comprise hydraulic cement. Insome cases it may be desirable for essentially all of the particleslarger than about 15 μm to comprise pozzolan and none to comprisehydraulic cement.

In still another embodiment, at least 50% of the combined pozzolan andhydraulic cement particles larger than about 10 μm (e.g., distributedover a range of about 10-100 μm, or about 10-60 μm) comprise pozzolanand less than 50% comprise hydraulic cement. Preferably, at least about65% of the particles larger than about 10 μm comprise pozzolan and lessthan about 35% comprise hydraulic cement. More preferably, at leastabout 75% of the particles larger than about 10 μm comprise pozzolan andless than about 25% comprise hydraulic cement. Even more preferably, atleast about 85% of the particles larger than about 10 μm comprisepozzolan and less than about 15% comprise hydraulic cement. Mostpreferably, at least about 95% of the particles larger than about 10 μmcomprise pozzolan and less than about 5% comprise hydraulic cement. Insome cases it may be desirable for essentially all of the particleslarger than about 10 μm to comprise pozzolan and none to comprisehydraulic cement.

In still another embodiment, at least 50% of the combined pozzolan andhydraulic cement particles larger than about 7.5 μm (e.g., distributedover a range of about 7.5-100 μm) comprise pozzolan and less than 50%comprise hydraulic cement. Preferably, at least about 65% of theparticles larger than about 7.5 μm comprise pozzolan and less than about35% comprise hydraulic cement. More preferably, at least about 75% ofthe particles larger than about 7.5 μm comprise pozzolan and less thanabout 25% comprise hydraulic cement. Even more preferably, at leastabout 85% of the particles larger than about 7.5 μm comprise pozzolanand less than about 15% comprise hydraulic cement. Most preferably, atleast about 95% of the particles larger than about 7.5 μm comprisepozzolan and less than about 5% comprise hydraulic cement. In some casesit may be desirable for essentially all of the particles larger thanabout 7.5 μm to comprise pozzolan and none to comprise hydraulic cement.

Finally, it may even be desirable in some cases that at least 50% of thecombined pozzolan and hydraulic cement particles larger than about 5 μm(e.g., distributed over a range of about 5-100 μm, or about 5-60 μm)comprise pozzolan and less than 50% comprise hydraulic cement.Preferably, at least about 65% of the particles larger than about 5 μmcomprise pozzolan and less than about 35% comprise hydraulic cement.More preferably, at least about 75% of the particles larger than about 5μm comprise pozzolan and less than about 25% comprise hydraulic cement.Even more preferably, at least about 85% of the particles larger thanabout 5 μm comprise pozzolan and less than about 15% comprise hydrauliccement. Most preferably, at least about 95% of the particles larger thanabout 5 μm comprise pozzolan and less than about 5% comprise hydrauliccement. In some cases it may be desirable for essentially all of theparticles larger than about 5 μm to comprise pozzolan and none tocomprise hydraulic cement.

According to one embodiment, at least about 75% of the combined pozzolanand hydraulic cement smaller than about 20 μm (e.g., distributed overthe range from about 0.1-20 μm) comprise hydraulic cement and less than25% comprise pozzolan. Preferably, at least about 80% of the particlessmaller than about 20 μm comprise hydraulic cement and less than about20% comprise pozzolan. More preferably, at least about 85% of theparticles smaller than about 20 μm comprise hydraulic cement and lessthan about 15% comprise pozzolan. Even more preferably, at least about90% of the particles smaller than about 20 μm comprise hydraulic cementand less than about 10% comprise pozzolan. Most preferably, at leastabout 95% of the particles smaller than about 20 μm comprise hydrauliccement and less than about 5% comprise pozzolan. In some cases it may bedesirable for essentially all of the particles smaller than about 20 μmto comprise hydraulic cement and none to comprise pozzolan.

In another embodiment, at least about 75% of the combined pozzolan andhydraulic cement particles smaller than about 15 μm (e.g., distributedover the range from about 0.1-15 μm) comprise hydraulic cement and lessthan 25% comprise pozzolan. Preferably, at least about 80% of theparticles smaller than about 15 μm comprise hydraulic cement and lessthan about 20% comprise pozzolan. More preferably, at least about 85% ofthe particles smaller than about 15 μm comprise hydraulic cement andless than about 15% comprise pozzolan. Even more preferably, at leastabout 90% of the particles smaller than about 15 μm comprise hydrauliccement and less than about 10% comprise pozzolan. Most preferably, atleast about 95% of the particles smaller than about 15 μm comprisehydraulic cement and less than about 5% comprise pozzolan. In some casesit may be desirable for essentially all of the particles smaller thanabout 15 μm to comprise hydraulic cement and none to comprise pozzolan.

In still another embodiment, at least about 75% of the combined pozzolanand hydraulic cement particles smaller than about 10 μm (e.g.,distributed over the range from about 0.1-10 μm) comprise hydrauliccement and less than 25% comprise pozzolan. Preferably, at least about80% of the particles smaller than about 10 μm comprise hydraulic cementand less than about 20% comprise pozzolan. More preferably, at leastabout 85% of the particles smaller than about 10 μm comprise hydrauliccement and less than about 15% comprise pozzolan. Even more preferably,at least about 90% of the particles smaller than about 10 μm comprisehydraulic cement and less than about 10% comprise pozzolan. Mostpreferably, at least about 95% of the particles smaller than about 10 μmcomprise hydraulic cement and less than about 5% comprise pozzolan. Insome cases it may be desirable for essentially all of the particlessmaller than about 10 μm to comprise hydraulic cement and none tocomprise pozzolan.

In still another embodiment, at least about 75% of the combined pozzolanand hydraulic cement particles smaller than about 7.5 μm (e.g.,distributed over the range from about 0.1-7.5 μm) comprise hydrauliccement and less than 25% comprise pozzolan. Preferably, at least about80% of the particles smaller than about 7.5 μm comprise hydraulic cementand less than about 20% comprise pozzolan. More preferably, at leastabout 85% of the particles smaller than about 7.5 μm comprise hydrauliccement and less than about 15% comprise pozzolan. Even more preferably,at least about 90% of the particles smaller than about 7.5 μm comprisehydraulic cement and less than about 10% comprise pozzolan. Mostpreferably, at least about 95% of the particles smaller than about 7.5μm comprise hydraulic cement and less than about 5% comprise pozzolan.In some cases it may be desirable for essentially all of the particlessmaller than about 7.5 μm to comprise hydraulic cement and none tocomprise pozzolan.

Finally, it may be desirable that at least about 75% of the combinedpozzolan and hydraulic cement particles smaller than about 5 μm (e.g.,distributed over the range from about 0.1-5 μm) comprise hydrauliccement and less than about 25% comprise pozzolan. Preferably, at leastabout 80% of the combined pozzolan and hydraulic cement particlessmaller than about 5 μm comprise hydraulic cement and less than about20% comprise pozzolan. More preferably, at least about 85% of theparticles smaller than about 5 μm comprise hydraulic cement and lessthan about 15% comprise pozzolan. Even more preferably, at least about90% of the particles smaller than about 5 μm comprise hydraulic cementand less than about 10% comprise pozzolan. Most preferably, at leastabout 95% of the particles smaller than about 5 μm comprise hydrauliccement and less than about 5% comprise pozzolan. In some cases it may bedesirable for essentially all of the particles smaller than about 5 μmto comprise hydraulic cement and none to comprise pozzolan.Notwithstanding the foregoing, in order to maintain sufficient earlystrength and reduce or prevent surface carbonation, it may be desirableto use a small quantity (e.g., about 0.5-3%) of a finely dividedpozzolan (e.g., silica fume, metakaoline or ground or classified flyash) having a particle size less than about 5 μm.

In order to further increase short-term strength development (e.g., 1-3days), it may be desirable in some cases to overload the pozzolan cementwith a higher quantity of very small hydraulic cement particles (i.e.,0.1-2.5 μm) in order to offset the strength retarding effect of thepozzolan particles. Accordingly, at least about 50% by weight of thehydraulic cement particles can have a particle size less than 2.5 μm(i.e., D₅₀ is 2.5 μm). In another embodiment, at least about 60% byweight of the hydraulic cement particles can have a particle size lessthan 2.5 μm (i.e., D₆₀ is 2.5 μm). In still embodiment, at least about70% by weight of the hydraulic cement particles can have a particle sizeless than 2.5 μm (i.e., D₇₀ is 2.5 μm). In yet another embodiment, atleast about 80% by weight of the hydraulic cement particles can have aparticle size less than 2.5 μm (i.e., D₈₀ is 2.5 μm). In some cases, theat least about 90% by weight of the hydraulic cement particles can havea particle size less than 2.5 μm (i.e., D₉₀ is 2.5 μm). In some cases,it may be possible for essentially all (at least about 99%) of thehydraulic cement particles to have a particle size of less than about2.5 μm.

The determination as to which particle size is selected as the cutoffbetween larger particles that are predominantly pozzolan and smallerparticles that are predominantly hydraulic cement depends on a number offactors. These include a desired reactivity, ratio of pozzolan tohydraulic cement, proportion of fine to coarse aggregates, use ofadmixtures, accelerants, retardants, hydration stabilizers, and fillers,and the like. In general, increasing the ratio of pozzolan to hydrauliccement can retard strength development while increasing the ratio ofhydraulic cement to pozzolan tends to accelerate strength development.Supplemental lime or other sources of calcium can accelerate setting, ascan increasing the relative quantity of very small hydraulic cementparticles (e.g., less than about 10 μm, or less than about 5 μm)compared to large cement and/or pozzolan particles (i.e., smallerhydraulic cement particles hydrate more rapidly than larger particles).Lye and other strong bases can also accelerate strength development byaccelerating the lime-pozzolan reaction (e.g., by increasing the rate bywhich silicate ions are leached from the pozzolan particles).

With respect to the relative proportions of pozzolan and hydrauliccement and particle size cutoff, according to one embodiment, a pozzolancement composition is provided in which at least at least 50%,preferably at least about 65%, more preferably at least about 75%, evenmore preferably at least about 85%, and most preferably at least about95% of the larger particles greater than about 20 μm comprise pozzolanand at least about 75%, preferably at least about 80%, more preferablyat least about 85%, even more preferably at least about 90%, and mostpreferably at least about 95% of the smaller particles less than about 5μm comprise hydraulic cement. According to other embodiments, the largerparticles associated with the applicable pozzolan ranges may includeparticles greater than about 15 μm, greater than about 10 μm, greaterthan about 7.5 μm, or greater than about 5 μm. According to otherembodiments, the smaller particles associated with the applicablehydraulic cement ranges may include particles less than about 7.5 μm,less than about 10 μm, less than about 15 μm, or less than about 20 μm.

In view of the foregoing, the pozzolan fraction will generally have anaverage particle size that exceeds the average particle size of thehydraulic (e.g., Portland) cement fraction. In general, the averageparticle size of the pozzolan fraction is in a range of about 1.25 timesto about 50 times the average particle size of the hydraulic cementfraction, preferably from about 1.5 times to about 30 times, morepreferably from about 1.75 times to about 20 times, and most preferablyfrom about 2 times to about 15 times the average particle size of thehydraulic cement fraction.

Stated another way, the Blaine fineness of the hydraulic cement fractionmay be about 1.25 times to about 50 times that of the pozzolan fraction,preferably 1.5 times to about 30 times, more preferably about 1.75 timesto about 20 times, and most preferably about 2 times to about 15 timesthe Blaine fineness of the pozzolan fraction. For example, the Blainefineness of the hydraulic cement fraction can be about 500 m²/kg orgreater, preferably about 650 m²/kg or greater, and more preferablyabout 800 m²/kg or greater, and the Blaine fineness of the pozzolanfraction can be about 325 m²/kg or less, preferably about 300 m²/kg orless, more preferably about 275 m²/kg or less.

The reactivity of the hydraulic cement fraction can be selected oradjusted to counterbalance the reactivity of the pozzolan fraction(e.g., by reducing or increasing the average particle size or finenessto increase or reduce reactivity, increasing or decreasing theproportion of tricalcium silicate relative to dicalcium silicate toincrease or decrease reactivity, increasing or reducing the quantity ofsupplemental lime, increasing or decreasing the quantity of gypsum, andthe like). For example, where the pozzolan is slower reacting, it may bedesirable to increase reactivity of the hydraulic cement fraction.Conversely, where the pozzolan is faster reacting, it may be desirableto decrease reactivity of the hydraulic cement fraction to maintain adesired overall reactivity. By adjusting the reactivity of the hydrauliccement fraction so as to best accommodate the reactivity of theavailable pozzolan, the present invention permits the manufacture ofpozzolan cement having a desired level of reactivity and early strengthdevelopment while using a wide variety of different available pozzolans.

In an embodiment of invention, a pozzolan cement composition is providedthat includes at least about 30% pozzolan and less than about 70%hydraulic cement (e.g., 55-70% hydraulic cement by volume and 30-45%pozzolan by volume). In another embodiment, a pozzolan cementcomposition is provided that includes at least about 40% pozzolan andless than about 60% hydraulic cement. In another embodiment, a pozzolancement composition is provided that includes at least about 45% pozzolanand less than about 55% hydraulic cement. In yet another embodiment, apozzolan cement composition is provided that includes at least about 55%pozzolan and less than about 45% hydraulic cement. In still anotherembodiment, a pozzolan cement composition is provided that includes atleast about 65% pozzolan and less than about 35% hydraulic cement. Andin another embodiment, a pozzolan cement composition is provided thatincludes at least about 75% pozzolan and less than about 25% hydrauliccement.

While the ranges provided herein relative to the particle sizedistributions of pozzolan and hydraulic cement are expressed in terms ofweight percent, in an alternative embodiment of the invention, theseranges can be expressed in volume percent. Converting weight percent tovolume percent may require using ratios of the densities of the variousmaterials. Moreover, to the extent a pozzolan contains a substantialquantity of calcium (e.g., CaO), it may be desirable to factor out theweight or volume of such calcium and consider it to be “supplementallime”.

In some cases, it may be desirable to include inert fillers in order toprovide a pozzolan cement having setting properties similar to OPC. Forexample, in the case where a relative high quantity of very smallhydraulic cement particles is used (e.g., D₅₀ less than 2.5 μm), thepozzolan cement may develop strength too quickly for some purposes. Inother words, the strength-accelerating effect of the hydraulic cementfraction may outweigh the strength retarding effect of the pozzolanfraction and set or harden too quickly. Rather than simply decrease theratio of hydraulic cement to pozzolan, it may be desirable to add aninert filler in order to provide increased spacing between the hydrauliccement particles and thereby slow down the initial setting time.According to one embodiment, the inert filler may include coarserparticles (e.g., 20-300 μm) in order to take up volume, increaseseparation of the hydraulic cement and/or pozzolan particles, and reducewater demand. According to another embodiment, the inert filler mayinclude finer particles (e.g., less than about 20 μm). The inert fillermay include inert fillers known in the art, examples of which includeground stone, rock and other geologic materials (e.g., ground granite,ground sand, ground bauxite, ground limestone, ground silica, groundalumina, and ground quartz).

B. Hydraulic Cement

“Portland cement” commonly refers to a ground particulate material thatcontains tricalcium silicate (“C₃S”), dicalcium silicate (“C₂S”),tricalcium aluminate (“C₃A”) and tetra-calcium aluminoferrite “(C₄AF”)in specified quantities established by standards such as ASTM C-150 andEN 197. The term “hydraulic cement”, as used herein, shall refer toPortland cement and related hydraulically settable materials thatcontain one or more of the four clinker materials (i.e., C₂S, C₃S, C₃Aand C₄AF), including cement compositions which have a high content oftricalcium silicate, cements that are chemically similar or analogous toordinary Portland cement, and cements that fall within ASTMspecification C-150-00.

In general, hydraulic cements are materials that, when mixed with waterand allowed to set, are resistant to degradation by water. The cementcan be a Portland cement, modified Portland cement, or masonry cement.“Portland cement”, as used in the trade, means a hydraulic cementproduced by pulverizing the large cement clinker particles (or nodules),comprising hydraulic calcium silicates, calcium aluminates, and calciumaluminoferrites, and usually containing one or more forms of calciumsulfate as an interground addition. Portland cements are classified inASTM C-150 as Type III, III, IV, and V. Other hydraulically settablematerials include ground granulated blast-furnace slag, hydraulichydrated lime, white cement, calcium aluminate cement, silicate cement,phosphate cement, high-alumina cement, magnesium oxychloride cement, oilwell cements (e.g., Type VI, VII and VIII), and combinations of theseand other similar materials. In a preferred embodiment, the Portlandcement has a chemical composition according to ASTM C-150 for Type I,II, or V cements, which tend to have beneficial properties for the readymix industry.

Portland cement is typically manufactured by grinding cement clinkerinto fine powder. Various types of cement grinders are currently used togrind clinker. In a typical grinding process, the clinker is grounduntil a desired fineness is achieved. The cement is also typicallyclassified to remove particles greater than about 45 μm in diameter,which are typically returned to the grinder for further grinding.Portland cements are typically ground to have a desired fineness andparticle size distribution between 0.1-100 μm, preferably 0.1-45 μm. Thegenerally accepted method for determining the “fineness” of a Portlandcement powder is the “Blaine permeability test”, which is performed byblowing air through an amount of cement powder and determining the airpermeability of the cement. This gives an approximation of the totalspecific surface area of the cement particles and also a roughapproximation of the particle size distribution, which is related to thespecific surface area.

In contrast to OPC, the inventive pozzolan cement does not utilize anormal distribution of Portland cement particles but rather smallerparticles as discussed above. All or a substantial portion of the largerhydraulic cement particles are “replaced” with similarly sized pozzolanparticles (e.g., which have the same or similar particle sizedistribution and/or fineness as the hydraulic cement particles theyreplace and/or have an average particle size that significantly exceedsthe average particle size of the hydraulic cement particles). Replacinglarger hydraulic cement particles with pozzolan particles reduces cost,overall CO₂ output, and deleterious effects caused by including too muchcement (e.g., creep, shrinkage, and decreased durability).

According to one embodiment, at least about 85% of the hydraulic cementparticles will have a particle size less than about 20 μm (e.g.,distributed over a range of about 0.1-20 μm), preferably at least about90%, more preferably at least about 95%, and most preferably at leastabout 99%. Stated another way, the D₈₅, D₉₀, D₉₅ or D₉₉ of the hydrauliccement particles is about 20 μm or less in this embodiment. Similarrestatements apply to the embodiments that follow. According to anotherembodiment, at least about 85% of the hydraulic cement particles willhave a particle size less than about 15 μm (e.g., distributed over arange of about 0.1-15 μm), preferably at least about 90%, morepreferably at least about 95%, and most preferably at least about 99%.According to yet another embodiment, at least about 85% of the hydrauliccement particles will have a particle size less than about 10 μm (e.g.,distributed over a range of about 0.1-10 μm), preferably at least about90%, more preferably at least about 95%, and most preferably at leastabout 99%. In still another embodiment, at least about 85% of thehydraulic cement particles will have a particle size less than about 7.5μm (e.g., distributed over a range of about 0.1-7.5 μm), preferably atleast about 90%, more preferably at least about 95%, and most preferablyat least about 99%. And in another embodiment, at least about 85% of thehydraulic cement particles will have a particle size less than about 5μm (e.g., distributed over a range of about 0.1-5 μm), preferably atleast about 90%, more preferably at least about 95%, and most preferablyat least about 99%.

C. Pozzolans

Pozzolans are usually defined as materials that contain constituentswhich will combine with free lime at ordinary temperatures in thepresence of water to form stable insoluble compounds possessingcementing properties. Pozzolans can be divided into two groups, naturaland artificial. Natural pozzolans are generally materials of volcanicorigin, but include diatomaceous earths. Artificial pozzolans are mainlyproducts obtained by heat treatment of natural materials such as clayand shale and certain siliceous rocks, and pulverized fuel ash (e.g.,fly ash).

Pozzolans of volcanic origin consist of glassy incoherent materials orcompacted tuffs arising from the deposition of volcanic dust and ash.They may occur in consolidated rock-like form underlying materialdeposited subsequently (e.g., Rhenish trass), or in a more fragmentaryand unconsolidated state (e.g., Italian pozzolans). Examples of naturalpozzolans include trass, perlite, Italian pozzolans, Santorin Earth,tosca, and tetin.

Rhenish trass is a trachytic (alkali feldspar) tuff which has beensubjected to the action of CO₂-bearing waters for such a long timeperiod that a large part of the minerals originally present has becomehydrated and decomposed. It consists of an isotropic ground masscontaining various crystalline mineral constituents such as feldspart,leucite and quartz, with small amounts of augite, hornblend, mica, andthe like. The glassy matrix, amounting to about half of the trass, isthe material that has undergone alternation and consists of zeoliticcompounds among which are analcite and chabazite or herschellite.

Santorin earth consists mainly of a granular isotropic material mixedwith pumice, obsidian and fragments of crystalline feldspar, pyroxenesand quartz, etc.

Natural volcanic pozzolans found in the United States are mostly tuffs,containing a rhyolitic glass with an index of refraction correspondingto a silica content of 70-76%. The glass content varies from about 50%to nearly 100%. The remaining constituents include quartz, feldspar,biotite, horneblende, hypersthene, sanidine, calcite and small amountsof opal, together with varying amounts of montmorillonite-type clays.

The chief artificial pozzolans are burnt clays and shales, spent oilshales, burnt gaize, burnt moler, pulverized fuel ash (e.g., fly ash),and ground slag. The product is ground to a desired fineness(conventionally to the same fineness as OPC).

Fly ash is a residue generated during combustion of coal. It isgenerally captured from the chimneys of coal-fired power plants, whereasbottom ash is removed from the bottom of the furnace. Depending upon thesource and makeup of the coal being burned, the components of the flyash produced vary considerably, but all fly ash includes substantialamounts of silicon dioxide (SiO₂) (both amorphous and crystalline) andwidely varying amounts of calcium oxide (CaO). Bottom ash is generallyless valuable than fly ash although it may be cleaned and ground toyield a useful pozzolan.

Fly ash material solidifies as glassy spheres or droplets whilesuspended in the exhaust gases and is collected by electrostaticprecipitators or filter bags. Since the particles solidify whilesuspended in the exhaust gases, fly ash particles are generallyspherical in shape and range in size from about 0.1-100 μm. They consistmostly of silicon dioxide (SiO₂), which is present in two forms:amorphous, which is rounded and smooth, and crystalline, which is sharp,pointed and hazardous; aluminum oxide (Al₂O₃) and iron oxide (Fe₂O₃).Fly ashes are generally highly heterogeneous, consisting of a mixture ofglassy particles with various identifiable crystalline phases such asquartz, mullite, and various iron oxides.

Two classes of fly ash are defined by ASTM C-618: Class F and Class C.The chief difference between these classes is the amount of calcium,silica, alumina, and iron content in the ash. Class F fly ash typicallycontains less than 10% lime (CaO); Class C fly ash generally containsmore than 20% lime (CaO). The chemical properties of the fly ash arelargely influenced by the chemical content of the coal burned (i.e.,anthracite, bituminous, and lignite). Not all fly ashes meet ASTM C-618requirements, although depending on the application, this may not benecessary. According to some standards, 75% of the fly ash must have afineness of 45 μm or less, and have a carbon content, measured by theloss on ignition (LOI), of less than 4%. The particle size distributionof raw fly ash can fluctuate constantly due to changing performance ofcoal mills and boiler performance. Fly ash used in concrete is oftenprocessed using separation equipment such as mechanical air classifiers.In the presence of water, Class C fly ash will harden and gain strengthover time. Unlike Class F, self-cementing Class C fly ash does notrequire an activator. Alkali and sulfate (SO₄) contents are generallyhigher in Class C fly ashes, which may make Class C fly ash lessattractive than Class F fly ash for concrete that may be prone to alkalior sulfate attack.

Blast furnace slag is a by-product obtained in the manufacture ofpig-iron in the blast furnace and is formed by the combination of theearthy constituents of the iron ore with the limestone flux. Thecomposition of slag can vary over a wide range depending on the natureof the ore, the composition of the limestone flux, the coke consumption,and the kind of iron being made. These variations affect the relativecontents of the four major constituents (lime, silica, alumina andmagnesia) and also the minor components (sulfur in the form of sulfide,and ferrous and manganese oxides). In general, the lime content mayrange from 30-50%, silica 28-38%, alumina 8-24%, magnesia 1-18%, sulfur1-2.5%, and ferrous and manganese oxides 1-3%, except in the specialcase of ferro-manganese production when the manganese oxide content ofthe slag may be considerably higher.

Besides the foregoing examples, any geologic material, both natural andartificial, which exhibits pozzolanic activity, can be used to make theinventive pozzolanic cements. Diatomaceous earth, opaline, cherts,clays, shales, fly ash, silica fume, volcanic tuffs, pumices, andtrasses are some of the known pozzolans. In order to reduce water demandand thereby improve strength while maintaining desired flow properties,pozzolans having more uniform surfaces (e.g., spherical or spheroidal)may be desirable. An example of a generally spherical pozzolan is flyash, owning to how it is formed. Ground pozzolans generally have morejagged morphologies, which can increase water demand. Therefore, to theextent a process is able to yield a pozzolan having a more uniformsurface, such a process would be desirable. In some cases, finerpozzolan particles can interact with and disperse fine cement particles,creating increased fluidity. Ultra fine pozzolans such as silica fumetypically decrease fluidity and increase water demand.

The lime (CaO) content within materials commonly considered to bepozzolanic in nature can vary greatly, as discussed above, from about 0%to about 50% by weight. According to one embodiment, the lime content ofthe pozzolan will be less than about 35% by weight. In anotherembodiment, the lime content will be less than about 25%. In yet anotherembodiment, the lime content will be less than about 15%. In stillanother embodiment, the lime content of the pozzolan will be less thanabout 10% by weight. In some cases it may be less than about 5%.

As discussed above, the particle size distribution of the pozzolanfraction with the inventive cements can be similar to that of the largerparticle fractions found in OPC (e.g., 10-45 μm). According to oneembodiment, at least about 85% of the pozzolan particles will have aparticle size greater than about 5 μm (e.g., distributed over a range ofabout 5-100 μm, or about 5-60 μm), preferably at least about 90%, morepreferably at least about 95%, and most preferably at least about 99%.Stated another way, the D₁₅, D₁₀, D₅ or D₁ of the pozzolan particles isabout 5 μm or greater in this embodiment. Similar restatements apply tothe embodiments that follow. In another embodiment, at least about 85%of the pozzolan particles will have a particle size greater than about7.5 μm (e.g., distributed over a range of about 7.5-100 μm, or about7.5-60 μm), preferably at least about 90%, more preferably at leastabout 95%, and most preferably at least about 99%. According to anotherembodiment, at least about 85% of the pozzolan particles will have aparticle size greater than about 10 μm (e.g., distributed over a rangeof about 10-100 μm, or about 10-60 μm), preferably at least about 90%,more preferably at least about 95%, and most preferably at least about99%. According to yet another embodiment, at least about 85% of thepozzolan particles will have a particle size greater than about 15 μm(e.g., distributed over a range of about 15-100 μm, or about 15-60 μm),preferably at least about 90%, more preferably at least about 95%, andmost preferably at least about 99%. And in another embodiment, at leastabout 85% of the pozzolan particles will have a particle size greaterthan about 20 μm (e.g., distributed over a range of about 20-100 μm, orabout 20-60 μm), preferably at least about 90%, more preferably at leastabout 95%, and most preferably at least about 99%.

Of course, it will be appreciated that a purpose of including largersized pozzolan particles is to reduce water demand. To the extent thiscan be accomplished using atypical particle size distributions not foundin OPC, such particle size distributions, so long as they fall withinone or more of the ranges set forth herein, would be within the scope ofthe invention. Thus, pozzolan particles that are distributed over anarrower range (e.g., over a range of about 20-60 μm, or about 25-50 μm,or about 30-40 μm) may be utilized. Notwithstanding the foregoing, asmall percentage of fine pozzolan particles (e.g., about 1-3 μm) may bedesirable to help disperse the fine cement particles and increasefluidity. Moreover, all things being equal, particles that are morespherical or uniform reduce water demand, which means that suchparticles can be smaller on average compared to more jagged particleswhile providing the same or lower water demand.

Depending on the particle size distribution of the starting pozzolanmaterial, it may be desirable to not only remove at least some of thefine pozzolan particles but also at least some of the coarsestparticles. For example, it may be desirable to remove a substantialportion (e.g., at least about 90%) of the particles greater than about120 μm, 100 μm, 80 μm, 60 μm or 45 μm. Accordingly, it may be desirablefor the pozzolan fraction to have a D₉₀ less than about 120 μm,preferably less than about 100 μm, more preferably less than about 80μm, even more preferably less than about 60 μm, and most preferably lessthan about 45 μm.

D. Supplemental Lime and Other Bases

As discussed above, hydraulic cements such as Portland cement whichcontain tricalcium silicate will typically provide excess calciumhydroxide that is available for reaction with the pozzolan. Depending onthe relative proportion of tricalcium silicate in the hydraulic cementand the relative quantity of hydraulic cement within the pozzolan cementcomposition, it may be desirable to include supplemental lime (e.g.,calcium oxide or calcium hydroxide) in order to provide additionalcalcium hydroxide for reaction with the pozzolan fraction. The amount ofsupplemental lime may vary from about 0-30% by weight of the overallpozzolan cement composition depending on the amount of pozzolan anddeficit of calcium, or about 2-25%, or about 5-20%.

Supplemental lime can be mixed up front with the pozzolan and hydrauliccement in order to yield a more lime balanced cement composition.Alternatively, some or all of the supplemental lime can be added to afresh concrete or other cementitious composition that includes pozzolancement within the scope of the invention. The same is true for otheradmixtures or fillers.

Other bases, such as magnesium oxide, magnesium hydroxide, alkali metaloxides, and alkali metal hydroxides can be added to accelerate thelime-pozzolan reaction.

III. Obtaining Particle Size Optimized Cement and Pozzolan

Any known method for obtaining hydraulic cement and fly ash having adesired particle size distribution and/or fineness can be used withinthe scope of the present invention. In general, particle size optimizedhydraulic cement can be obtained by grinding and classifying cementclinker so as to have a desired particle size distribution.

FIG. 1 illustrates a system 100 for carrying out the methods describedherein. In one embodiment, an initial stream of pozzolan particles(e.g., with particle sizes distributed over a range of about 0.1-100 μm)can be stored in silo 110. An initial stream of hydraulic cementparticles (e.g., Portland cement with particle sizes distributed over arange of about 0.1-45 μm) can be stored in silo 112. The initialpozzolan stream is delivered to an air classifier 114 and a top cut at adesired D₉₀ (e.g., about 45 μm) is performed. Particles above the topcut (e.g., about 45 μm) can then be ground to yield particles smallerthan the top cut in grinder 116 in a closed circuit indicated by arrows118. Classifier 114 and/or a second classifier (not shown) can be usedto dedust the pozzolan to remove at least some of the particles lessthan a desired D₁₀ (e.g., about 10 μm) if the pozzolan source is finerthan desired. The modified stream of pozzolan particles between thebottom cut and top cut (e.g., distributed over a range of about 10-45μm) are then delivered to mixer 120 for mixing.

The initial stream of hydraulic cement from silo 112 is delivered to airclassifier 122 and cut at a desired D₉₀ (e.g., about 10 μm). The finecement particles are delivered to mixer 120 and the coarse cementparticles are delivered to grinder 124 and ground in a closed circuit asindicated by arrows 126 to achieve a particle size distribution havingthe desired D₉₀ (e.g., about 10 μm). The ground cement particles arealso delivered to mixer 120 and mixed to produce the blended pozzolancement. The classified and ground cement particles comprise a modifiedstream of hydraulic cement particles. Mixer 120 can be any blendingapparatus known in the art or can even be a grinder. In the case wheremixer 120 is also a grinder, some reduction in the particle sizes ofcement and pozzolan would be expected although the amount of grindingcan be selected, or even minimized, to mainly ensure intimate mixing ofthe cement and pozzolan particles rather than grinding. The pozzolancement blend from mixer 120 can then be delivered to one or more storagehoppers 128 for later use or distribution.

System 100 can be used to produce cement particles and pozzolanparticles within any of the particle size distribution ranges describedin this application. In addition, system 100 can include more or fewergrinders and classifiers, conduits, bag houses, analyticalinstrumentation, and other hardware known in the art. Hydraulic cementand pozzolan particles can be stored and moved in system 100 using anytechniques known in the art, including conveyors, pneumatic systems,heavy equipment, etc. The hydraulic cement can be provided as groundcement or as clinker. As such, system 100 can be incorporated into afinish mill as understood in the cement art. In addition, system 100 canuse open circuit milling in addition to or as an alternative to closedcircuit milling. While system 100 shows the coarsest pozzolan particlesbeing reground, those skilled in the art will recognize that pozzolan isoften a waste material and the use of the removed coarse and finepozzolan fractions is not necessary.

According to one embodiment, hydraulic cement clinker can be groundaccording to known methods, such as using a rod mill and/or ball mill.Such methods typically yield cement having a wide particle sizedistribution of about 0.1-100 μm. Thereafter, the ground cement ispassed through an air classifier in order to separate the fine particlefraction. The coarse fraction can be returned to the grinder and/orintroduced into a dedicated grinder in order to regrind the coarsefraction. The reground cement material is then passed through an airclassifier in order to separate the fine particle fraction. The finefraction from the second classification step can be blended with thefine fraction from the first classification step. This process can berepeated until all the cement has been ground and classified to adesired particle size distribution. Repeatedly classifying the groundcement, regrinding the coarse fraction, and blending together the finefractions advantageously yields a fine cement material havingsubstantially the same chemistry as the clinker from which it is made.Grinding aids and blending components (e.g., gypsum) known in the artcan be added during or after the grinding process.

In an alternative embodiment, finished hydraulic cement such as OPC canbe classified in order to separate the fine fraction from the coarsefraction, regrinding the coarse fraction, classifying the regroundmaterial, and blending the first and second fine fractions. This processcan be repeated until all the cement has been ground and classified tothe desired particle size distribution. Repeatedly classifying theground cement, regrinding the coarse fraction, and blending together thefine fractions advantageously yields a fine cement material havingsubstantially the same chemistry as the original hydraulic cement. Byway of example, the first classification step might concentrate gypsumin the fine fraction, as gypsum is often concentrated in the fineparticle fraction of OPC. Regrinding the coarse fraction and blendingthe newly obtained fine fraction(s) with the original fine fraction canrestore the original balance of gypsum to calcium silicates andaluminates.

The pozzolan fraction (e.g., fly ash), to the extent it contains anundesirable quantity of very fine and/or very coarse particles, cansimilarly be classified using an air classifier in order to remove atleast a portion of the very fine and/or very coarse particles. Verycoarse pozzolan particles (e.g., greater than about 60-120 μm) removedduring classification can be ground or otherwise treated (e.g., by otherfracturing methods known in the art) so as to fall within the desiredparticle size distribution. Very fine pozzolan particles (e.g., lessthan about 10 μm) removed during the classification process can be soldto end users (e.g., grout manufacturers) as is or further ground into anultra-fine product (e.g., less than about 1 μm) so as to yield a highlyreactive pozzolan material that can act as a substitute for relativelyexpensive pozzolans such as silica fume and metakaolin used to form highstrength concretes with decreased pore permeability.

Other methods for obtaining hydraulic cement and pozzolan fractionshaving a desired particle size distribution and/or fineness can be used,such as mechanical sieves. However, such methods are usually much slowerand more expensive than high volume air classification.

As mentioned above, the pozzolan cement blends of the invention cansubstitute for OPC, including Type I and Type II cements. Type I andType II cements are commonly terms used to refer to a binder withcharacteristics defined by ASTM C-150. As those skilled in the art willappreciate, general purpose blended cements that can substitute for ASTMC150 cement should have set times and other performance characteristicsthat fall within the ranges of ASTM C-150 in order to serve as asubstitute for Type I or Type II cement in the ready mix industry. Inone embodiment, the blended cement meets the fineness and/or set timerequirements of a Type I/II OPC, as defined in ASTM C-150-08 orC-150-00, which are both incorporated herein by reference. In oneembodiment, the pozzolan cement blends of the invention have a finenessin a range from about 200 m²/kg to about 650 m²/kg, more preferablyabout 280 m²/kg to about 600 m²/kg, even more preferably about 300 m²/kgto about 500 m²/kg, and most preferably about 350 m²/kg to about 450m²/kg.

In a preferred embodiment, the set time of the pozzolan cementcomposition is within the ASTM C-150 standard for set time, which uses aVicat test according to C-191, which is also incorporated herein byreference. In one embodiment, the initial set time is in a range fromabout 30 minutes to about 500 minutes, more preferably about 45 minutesto about 375 minutes, and most preferably about 60 minutes to about 350minutes.

In one embodiment, the pozzolan cement has an autoclave expansion max %as defined by C-151, which is also hereby incorporated herein byreference, of less than 0.9, more preferably 0.80.

In one embodiment, the pozzolan cement meets the compressive strengthtest of Type I/II cements according to ASTM C-150, which definesstrength according to ASTM C-109, which is hereby incorporated byreference. In one embodiment, the 3-day strength of the pozzolan cementblend is at least about 10 MPa, more preferably at least about 12 MPa.In one embodiment, the 7-day strength of the pozzolan cement blend is atleast about 17 MPa, more preferably at least about 19 MPa. In oneembodiment, the 28-day strength of the pozzolan cement blend is at leastabout 28 MPa, more preferably at least about 32 MPa.

As mentioned above, in one embodiment, the pozzolan cement blends havesimilar performance characteristics of Type I/II cement rather than TypeIII cement, which is a rapid hardening cement and not generally asbeneficial for the ready mix industry. Where type I/II cement ismimicked, the early strength is preferably less than that of type IIIcement, which will result in better long term strength. In thisembodiment, the 1-day strength of the pozzolan cement blend, accordingto ASTM C109, is preferably less than about 15 MPa, more preferably lessthan about 12 MPa, and most preferably less than about 10 MPa, and the3-day strength is preferably less than about 24 MPa, more preferablyless than about 22 MPa, and most preferably less than about 19 MPa.

The pozzolan cement blend may have any other features of Type I or TypeII cement as set forth in ASTM C-150. In addition, the pozzolan cementblend may have any features set forth in ASTM C-595-08 for blendedcements. In one embodiment, the maximum weight percent of pozzolan inthe pozzolan cement blend of the invention can be about 40% or less.Limiting the weight percent of pozzolan can minimize the effects ofvariable chemistry in the most pozzolan sources.

The pozzolan cement blends of the invention may have any of theforegoing characteristics of Type I/II cements in any combination. TheseASTM related features can be used in any combination with the particlesize distribution ranges described above.

IV. Cementitious Compositions

The inventive pozzolan cement compositions can be used to make concrete,mortar, grout, molding compositions, or other cementitious compositions.In general, “concrete” refers to cementitious compositions that includea hydraulic cement binder and aggregate, such as fine and coarseaggregates (e.g., sand and rock). “Mortar” typically includes cement,sand and lime and can be sufficiently stiff to support the weight of abrick or concrete block. “Grout” is used to fill in spaces, such ascracks or crevices in concrete structures, spaces between structuralobjects, and spaces between tiles. “Molding compositions” are used tomanufacture molded or cast objects, such as pots, troughs, posts,fountains, ornamental stone, and the like.

Water is both a reactant and rheology modifier that permits freshconcrete, mortar or grout to flow or be molded into a desiredconfiguration. The hydraulic cement binder reacts with water, is whatbinds the other solid components together, and is responsible forstrength development. Cementitious compositions within the scope of thepresent invention will typically include hydraulic cement (e.g.,Portland cement), pozzolan (e.g., fly ash), water, and aggregate (e.g.,sand and/or rock). Other components that can be added include water andoptional admixtures, including but not limited to accelerating agents,retarding agents, plasticizers, water reducers, water binders, and thelike.

It will be appreciated that the inventive pozzolan cement compositionscan be manufactured (i.e., blended) prior to incorporation into acementitious composition or they may be prepared in situ. For example,some or all of the hydraulic cement and pozzolan particles can be mixedtogether when making a cementitious composition. In the case wheresupplemental lime is desired in order to increase the speed and/orextent of pozzolan hydration, at least some of the supplemental lime orother base may be added to the cementitious composition directly.

In order to accelerate hydration of the pozzolan fraction, it may bedesirable to pre-treat at least some of the pozzolan particles withaqueous calcium hydroxide or other basic solutions in order to commencehydration prior to exposing the hydraulic cement particles to water.This may be helpful in closing the time gap of hydration between themore quickly reacting hydraulic cement particles and more slowlyreacting pozzolan particles. For example, at least a portion of thepozzolan fraction can be mixed with aqueous calcium hydroxide at leastabout 30 minutes prior to exposing the hydraulic cement fraction towater. Alternatively, the pozzolan can be mixed with aqueous calciumhydroxide at least about 1 hour, at least about 3 hours, at least about5 hours, or at least about 8 hours prior to exposing the hydrauliccement to water.

Depending on the relative reactivity of the hydraulic cement and ratioof hydraulic cement to pozzolan, it may be desirable to accelerate orretard hydration. In the case where the hydraulic cement particles (e.g.greater than about 50%) have a very small average particle size (e.g.,less than about 5 μm, about 3 μm, or about 1 μm) in order to impart highearly strength, it may be desirable to include a hydration stabilizerthat can retard setting and prevent flash setting and/or rapidhardening. The use of a hydration stabilizer may permit the use of verysmall hydraulic cement particles in order to achieve high early strengthwhile preventing uncontrollable or flash setting.

A “hydration stabilizer” (also known as an extended set retarder) can beused to inhibit the hydration of the hydraulic cement. The most commonlyused hydration stabilizer is gypsum, which inhibits hydration oftricalcium aluminate and prevents flash setting through formation ofettringite with the tricalcium aluminate. According to one embodiment,it may be desirable to increase or decrease the amount of gypsum basedon the quantity of fast reacting tricalcium aluminate and otheraluminates in the hydraulic cement and/or pozzolan and/or hydrauliccement/pozzolan mix. Increasing the gypsum retards setting of thealuminates. Decreasing the gypsum accelerates setting of the aluminates.It may be desirable to optimize the quantity of gypsum for differentpozzolan cement blends to achieve a desired set time for each blend.

Other types of hydration stabilizers slow the rate of hydrate formationby tying up (i.e., chelating, complexing, or otherwise binding) calciumions on the surface of the hydraulic cement particles. Examples ofhydration stabilizers include polyphosphonic acids or carboxylic acidsthat contain hydroxyl and/or amino groups.

In some cases, it may desirable to include an accelerator. Acceleratorsthat can be used to activate the hydraulic cement can be selected fromconventional cement accelerators such as those classified as ASTM C 494Type C admixtures. These include alkaline earth metal halides (calciumchloride and the like), alkaline earth metal nitrites (calcium nitriteand the like), alkaline earth metal nitrates (calcium nitrate and thelike), alkaline earth metal formates (calcium formate and the like),alkali metal thiocyanates (sodium thiocyanate and the like),triethanolamine and the like. The amount, based on hydraulic cementcontent (i.e., exclusive of the pozzolan), should be from about 0.5-6%by weight, preferably from about 1-5% by weight.

Water reducers may be particularly useful in order to increaseflowability of the cementitious compositions and/or reduce water demand.Conventional, mid-range, and high-range water reducers can be used.Conventional water reducers can be used to achieve a minimum waterreduction of 5% and/or an increase in slump of about 1-2 inches.Mid-range water reducers can reduce water demand by 8-15%. High-rangewater reducers can reduce water demand by 12-40%. Mid-range andhigh-range water reducers also can be used to slow the setting ofconcrete in hot weather.

V. Examples

The following examples, when expressed in the past tense, illustrateembodiments of the invention that have actually been prepared. Examplesgiven in the present tense are hypothetical in nature but arenevertheless illustrative of embodiments within the scope of theinvention.

Cementitious mortar compositions were prepared according to ASTM C-109in order to test the strength of mortar cubes made therefrom. The mortarcompositions were prepared according to standard procedures establishedby ASTM C-109, including adding the cement to the water, mixing at slowspeed for 30 seconds, adding the sand over a period of 30 seconds whilemixing at slow speed, stopping the mixing, scraping the walls, lettingthe mixture stand for 90 seconds, and then mixing at medium speed for 60seconds.

The flow of each of the cementitious mortar compositions was testedusing a standard flow table, in which a sample of mortar was placed inthe middle of the table, the table was subjected to 25 raps, and thediameter of the resulting mass was measured in four directions and addedtogether to give a composite flow value in centimeters.

Thereafter, the mortar was packed into mortar cube molds using standardprocedures established by ASTM C-109, including filling the moldshalf-way, compacting the mortar in the molds using a packing tool,filling the molds to the tops, compacting the mortar using a packingtool, and smoothing off the surface of mortar in the molds.

The mortar cube molds were placed in a standard humidity chamber for 1day. Thereafter, the mortar cubes were removed from the molds andsubmerged inside buckets filled with saturated aqueous lime solution.The cubes were thereafter tested for compressive strength using astandard compressive strength press at 3 days, 7 days and 28 days.

Examples 1-4

Examples 1-4 illustrate the effect of particle size optimizing a 70:30blend of Portland cement and fly ash. The Portland cement used in eachof Examples 1-4 was Type II made by grinding Type V cement more finely.Example 1 was a particle size optimized 70:30 cement/pozzolan blend. Itemployed a classified Portland cement identified as “cement #11”, whichwas obtained by passing Type II Portland cement through a Microsizer AirClassifier manufactured by Progressive Industries, located in Sylacauga,Ala. and collecting the fine fraction. Example 1 also employedclassified fly ash identified as “fly ash 8z1”, which was obtained bypassing Class F fly ash through an air classifier twice, first to removemost of the fines below about 10 μm and second to remove most of thefines above about 50 μm. The air classifier was model CFS 8 HDS ofNetzsch-Condux Mahltechnik GmbH, located in Hanau, Germany. Examples 2and 3 were both 70:30 control blends of Portland cement and fly ashwhich used unclassified Type II cement (“control cement”) and Class Ffly ash (“control fly ash”). Example 4 used 100% ordinary Type IIPortland cement. The particle size distributions of the Portland cementand fly ash fractions were determined at Netzsch-Condux Mahltechnik GmbHusing a Cilas 1064 particle size analyzer and are set forth below inTable 1.

TABLE 1 Percent Passing/Cumulative Total (%) Particle Size Control (μm)Cement #11 cement Fly Ash 8z1 Control fly ash 0.04 0.15 0.13 0.04 0.100.10 0.84 0.81 0.09 0.51 0.50 5.27 5.79 0.68 3.40 1.00 12.71 13.44 1.919.27 2.00 21.97 21.21 3.36 20.74 3.00 28.13 24.99 3.88 28.59 4.00 35.7629.24 4.22 33.79 6.00 54.90 39.23 4.69 40.87 8.00 73.49 48.47 4.69 46.2710.00 87.10 56.15 4.69 50.78 15.00 99.13 71.34 10.04 59.32 20.00 100.083.16 24.65 65.58 32.00 100.0 97.50 66.84 78.82 50.00 100.0 100.0 95.5393.78 71.00 100.0 100.0 100.0 99.40 100.0 100.0 100.0 100.0 100.0

The compositions used in making mortar cubes according to Examples 1-4and also the flow and strength results are set forth below in Table 2.The amount of fly ash added to the 70:30 blends was reduced to accountfor its reduced density compared to the Portland cement in order tomaintain 30% volumetric replacement.

TABLE 2 Component/ Example strength 1 2 3 4 Cement #11 518 g — — — FlyAsh 8z1 162.1 g — — — Control OPC — 518 g 518 g 740 g Control FA — 162.1g 162.1 g — Graded Sand 2035 g 2035 g 2035 g 2035 g Water 360 g 360 g330 g 360 g Flow 106 136+* 109.5 118 3-day strength 26.6 MPa 16.0 MPa15.8 MPa 28.6 MPa 7-day strength 26.8 MPa 21.2 MPa 18.2 MPa 32.4 MPa28-day strength 40.9 MPa 32.0 MPa 35.4 MPa 45.6 MPa *Only 21 taps onflow table

As can be seen from the data in Table 2, the inventive 70:30 blend ofExample 1 had 93% of the strength of the 100% OPC composition of Example4 at 3 days, 83% of the strength at 7 days, and 90% of the strength at28 days. By comparison, the 70:30 control blends of Examples 2 and 3only had 56% and 55%, respectively, of the strength of the 100% OPCcomposition of Example 4 at 3 days, 65% and 56%, respectively, of thestrength at 7 days, and 70% and 78% of the strength at 28 days. Particlesize optimizing the Portland cement and fly ash fractions yieldedsubstantially greater strength development compared to the controlblends at 3, 7 and 28 days. The increase in strength was particularlypronounced at 3 days. FIG. 2 graphically illustrates and compares thestrengths obtained using the compositions of Examples 1-4

Examples 5-14

Other mortar compositions (i.e., 60:40 and 70:30 blends) weremanufactured using cement #11 and fly ash 8z1. In addition, mortarcompositions were manufactured using another classified cement materialidentified as “cement #13” and another classified fly ash identified as“fly ash 7G”. Cement #13 was classified at the same facility as cement#11. The particle size distributions of cement #11, cement #13 and thecontrol cement were determined at the classifying facility using aBeckman Coulter LS 13 320 X-ray diffraction analyzer and are set forthbelow in Table 3.

TABLE 3 Particle Size Percent Passing/Cumulative Total (%) (μm) Cement#11 Cement #13 Control cement 0.412 0.26 0.33 0.14 0.545 2.33 2.96 1.240.721 6.42 8.21 3.43 0.954 11.9 15.3 6.37 1.261 18.1 23.5 9.66 1.66924.7 32.5 13.0 2.208 32.1 42.1 16.6 2.920 40.9 52.7 20.5 3.863 51.6 64.225.3 5.111 64.1 76.1 31.5 6.761 77.4 87.3 39.4 8.944 89.6 96.0 49.011.83 97.9 99.8 60.3 15.65 99.97 100 73.0 20.71 100 100 85.6 24.95 100100 92.4 30.07 100 100 96.7 36.24 100 100 98.9 43.67 100 100 99.8 52.63100 100 99.995

Fly ash 7G was classified at the same facility as fly ash 8z1(Netzsch-Condux Mahltechnik GmbH) but was only classified once to removefine particles. It was not classified a second time to remove coarseparticles. The particle size distribution of fly ash 7G was determinedusing a Cilas 1064 particle size analyzer and is set forth below inTable 4. The PSD of the control fly ash is included for comparison

TABLE 4 Particle Size Percent Passing/Cumulative Total (%) (μm) Fly Ash7G Control fly ash 0.04 0.00 0.10 0.10 0.00 0.51 0.50 0.51 3.40 1.001.34 9.27 2.00 2.24 20.74 3.00 2.60 28.59 4.00 2.80 33.79 6.00 2.9940.87 8.00 2.99 46.27 10.00 2.99 50.78 15.00 5.26 59.32 20.00 10.9465.58 32.00 29.26 78.82 50.00 54.79 93.78 71.00 76.18 99.40 100.0 92.01100.0 150.0 99.46 100.0

The compositions used in making mortar cubes according to Examples 5-14and also the flow and strength results are set forth below in Tables 5and 6. The amount of fly ash added to some of the blends was reduced toaccount for its reduced density compared to the Portland cement in orderto maintain a 30% or 40% volumetric replacement. In other cases, thereplacement was 30% or 40% by weight. In one example, lye was added; inanother, slaked lime.

TABLE 5 Component/ Example strength 5 6 7 8 9 Cement #11 444 g 518 g 444g 444 g 444 g Cement #13 — — — — — Fly Ash 8z1 — — 216.1 g — — Fly Ash7G 296 g 222 g — 216.1 g — Control FA — — — — 216.1 g Graded Sand 2035 g2035 g 2035 g 2035 g 2035 g Water 390 g 370 g 360 g 360 g 360 g Flow 10995 122 110 107.5  3-day 19.1 MPa 26.1 MPa 19.4 MPa 16.7 MPa 20.7 MPa 7-day 21.5 MPa 33.0 MPa 26.7 MPa 25.3 MPa 21.8 MPa 28-day 28.2 MPa 35.5MPa 28.2 MPa 30.3 MPa 25.9 MPa

TABLE 6 Component/ Example strength 10 11 12 13 14 Cement #11 444 g —518 g 444 g 444 g Cement #13 — 444 g — — — Fly Ash 8z1 216.1 g 216.1 g162 g — — Fly Ash 7G — — — 216.1 g 216.1 g Type S Lime — — — — 20 g NaOH3.3 g — Graded Sand 2035 g 2035 g 2035 g 2035 g 2035 g Water 350 g 360 g360 g 360 g 360 g Flow 106.5 110.5 86.5 89 98  3-day 19.7 MPa 18.7 MPa19.9 MPa 17.9 MPa 17.9 MPa  7-day 20.9 MPa 21.9 MPa 25.9 MPa 19.1 MPa17.6 MPa 28-day 27.6 MPa 30.6 MPa 28.6 MPa 23.7 MPa 28.6 MPa

The following examples are hypothetical examples based on the principalsdisclosed herein.

Example 15

A high early strength pozzolan cement is manufactured by combining thefollowing components in the amounts specified:

Component Amount by Weight Particle Size Range Portland cement 45%0.1-20 μm Pozzolan 50% 20-100 μm Calcium hydroxide  5% 1-10 μm

The foregoing composition has early strength that is comparable to OPCand a strength and durability after 1 year that equals or exceeds thatof OPC.

Example 16

A high early strength pozzolan cement is manufactured by combining thefollowing components in the amounts specified:

Component Amount by Weight Particle Size Range Portland cement 40%0.1-15 μm Pozzolan 53% 15-100 μm Calcium hydroxide  7% 1-10 μm

The foregoing composition has early strength that is comparable to OPCand a strength and durability after 1 year that equals or exceeds thatof OPC.

Example 17

A high early strength pozzolan cement is manufactured by combining thefollowing components in the amounts specified:

Component Amount by Weight Particle Size Range Portland cement 30%0.1-10 μm Pozzolan 60% 10-100 μm Calcium hydroxide 10% 1-10 μm

The foregoing composition has early strength that is comparable to OPCand a strength and durability after 1 year that equals or exceeds thatof OPC.

Example 18

A high early strength pozzolan cement is manufactured by combining thefollowing components in the amounts specified:

Component Amount by Weight Particle Size Range Portland cement 20% 0.1-5μm Pozzolan 65% 10-100 μm Calcium hydroxide 15% 1-10 μm

The foregoing composition has early strength that is comparable to OPCand a strength and durability after 1 year that equals or exceeds thatof OPC.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A pozzolan cement composition comprising: a hydraulic cement fractioncomprised of a distribution of differently sized hydraulic cementparticles at least partially comprised of tricalcium silicate and/ordicalcium silicate that provide excess calcium hydroxide, when mixedwith water, that is available for reaction with a pozzolan, thehydraulic cement fraction having a Blaine fineness greater than about500 m²/kg; and a pozzolan fraction comprised of a distribution ofdifferently sized pozzolan particles capable of reacting with calciumhydroxide in the presence of water, including calcium hydroxide providedby the hydraulic cement particles when mixed with water, in order toform solid hydration products having cementitious properties, thepozzolan fraction having a Blaine fineness that is less than the Blainefineness of the hydraulic cement fraction, wherein a majority of thecombined hydraulic cement and pozzolan particles above 20 μm arepozzolan particles and a majority of the combined hydraulic cement andpozzolan particles below 20 μm are hydraulic cement particles.
 2. Apozzolan cement composition as in claim 1, wherein the Blaine finenessof the hydraulic cement fraction is about 1.25 times to about 50 timesgreater than the Blaine fineness of the pozzolan fraction.
 3. A pozzolancement composition as in claim 1, wherein the Blaine fineness of thehydraulic cement fraction is about 1.5 times to about 30 times greaterthan the Blaine fineness of the pozzolan fraction.
 4. A pozzolan cementcomposition as in claim 1, wherein the Blaine fineness of the hydrauliccement fraction is about 1.75 times to about 20 times greater than theBlaine fineness of the pozzolan fraction.
 5. A pozzolan cementcomposition as in claim 1, wherein the Blaine fineness of the hydrauliccement fraction is about 2 times to about 15 times greater than theBlaine fineness of the pozzolan fraction.
 6. A pozzolan cementcomposition as in claim 1, wherein the Blaine fineness of the hydrauliccement fraction is greater than about 650 m²/kg.
 7. A pozzolan cementcomposition as in claim 1, wherein the Blaine fineness of the hydrauliccement fraction is greater than about 800 m²/kg.
 8. A pozzolan cementcomposition as in claim 1, wherein hydraulic cement fraction has afineness so as to qualify as Type III Portland cement but with a slowerset time and lower water demand as a result of being blended with thepozzolan fraction.
 9. A pozzolan cement composition as in claim 1,wherein the pozzolan cement composition has a set time similar to thatof Type I or Type II Portland cement according to ASTM C-150.
 10. Apozzolan cement composition as in claim 1, wherein the Blaine finenessof the pozzolan fraction is less than about 325 m²/kg.
 11. A pozzolancement composition as in claim 1, wherein the Blaine fineness of thepozzolan fraction is less than about 300 m²/kg.
 12. A pozzolan cementcomposition as in claim 1, wherein the hydraulic cement fraction andpozzolan fraction have a combined Blaine fineness in a range of about280 m²/kg to about 600 m²/kg.
 13. A pozzolan cement composition as inclaim 1, wherein the hydraulic cement fraction and pozzolan fractionhave a combined Blaine fineness fineness in a range of about 300 m²/kgto about 500 m²/kg.
 14. A pozzolan cement composition as in claim 1,wherein the hydraulic cement particles have a D₈₅ less than about 20 μm,and wherein at least about 65% of the combined pozzolan and cementparticles larger than about 20 μm comprise pozzolan particles and lessthan about 35% of the combined pozzolan and cement particles larger thanabout 20 μm comprise hydraulic cement particles.
 15. A pozzolan cementcomposition as in claim 1, wherein the hydraulic cement particles havinga D₉₀ less than about 20 μm, and wherein at least about 75% of thecombined pozzolan and cement particles larger than about 20 μm comprisepozzolan particles and less than about 25% of the combined pozzolan andcement particles larger than about 20 μm comprise hydraulic cementparticles.
 16. A pozzolan cement composition as in claim 1, wherein thehydraulic cement particles have a D₉₀ less than about 15 μm, and whereinat least about 75% of the combined pozzolan and cement particles largerthan about 15 μm comprise pozzolan particles and less than about 25% ofthe combined pozzolan and cement particles larger than about 15 μmcomprise hydraulic cement particles.
 17. A pozzolan cement compositionas in claim 1, wherein the pozzolan particles comprise at least 30% byvolume of combined pozzolan and hydraulic cement particles and thehydraulic cement particles comprise up to 70% by volume of the combinedpozzolan and hydraulic cement particles.
 18. A pozzolan cementcomposition as in claim 1, wherein the hydraulic cement fraction andpozzolan fraction form a dry blend of particles with no added water. 19.A pozzolan cement composition as in claim 1, wherein the pozzolanparticles comprise at least one component selected from the groupconsisting, pulverized fuel ash, of ash produced from coal combustion,class F fly ash, class C fly ash, ground slag, materials of volcanicorigin, trass, and diatomaceous earth, burnt clays, burnt shales, spentoil shales, burnt gaize, and burnt moler.
 20. A pozzolan cementcomposition as in claim 1, wherein the dry blend further includes atleast one component selected from the group consisting of fineaggregates, coarse aggregates, inert fillers, lime, lye, water reducingadmixtures, accelerants, retardants, hydration stabilizers, andrheology-modifying agents.
 21. A pozzolan cement composition as in claim1, further comprising water so as to form a fresh cementitiouscomposition.
 22. A pozzolan cement composition as in claim 21, whereinthe fresh cementitious composition is fresh concrete that furtherincludes fine aggregate, coarse aggregate and at least one of inertfiller, lime, lye, water reducing admixture, accelerant, retardant,hydration stabilizer, or rheology-modifying agent.
 23. A pozzolan cementcomposition as in claim 22, wherein the fresh concrete has a Vicatinitial set time in a range of about 45-375 minutes and a maximumautoclave expansion of about 0.8%.
 24. A method of manufacturing thepozzolan cement composition of claim 1, comprising: obtaining thehydraulic cement fraction; obtaining the pozzolan fraction; andcombining the hydraulic cement fraction and the pozzolan fraction toyield the pozzolan cement composition.
 25. A method as in claim 24,wherein the hydraulic cement fraction is combined with the pozzolanfraction in a manner so as to yield a dry blend of particles.
 26. Amethod as in claim 25, further comprising combining the dry blend ofparticles with water to form a fresh cementitious composition selectedfrom the group consisting of concrete, mortar, grout, and moldingcompositions.
 27. A method as in claim 26, wherein forming the freshcementitious composition includes adding fine aggregate, coarseaggregate and at least one of inert filler, lime, lye, water reducingadmixture, accelerant, retardant, hydration stabilizer, orrheology-modifying agent to form fresh concrete.
 28. A method as inclaim 24, wherein the hydraulic cement fraction is combined with thepozzolan fraction and water in situ to yield a fresh cementitiouscomposition selected from the group consisting of concrete, mortar,grout, and molding compositions.
 29. A method as in claim 28, whereinforming the fresh cementitious composition includes adding fineaggregate, coarse aggregate and at least one of inert filler, lime, lye,water reducing admixture, accelerant, retardant, hydration stabilizer,or rheology-modifying agent to form fresh concrete.
 30. A method as inclaim 28, further comprising pre-treating at least a portion of thepozzolan fraction with an aqueous base prior to exposing the hydrauliccement fraction to water.
 31. A pozzolan cement composition comprising:a Portland cement fraction comprised of a distribution of differentlysized Portland cement particles having a chemistry and a Blaine finenessso that the Portland cement fraction either qualifies as a Type IIIPortland cement under ASTM C-150 or is finer than a Type III Portlandcement under ASTM C-150; and a pozzolan fraction comprised of adistribution of differently sized pozzolan particles blended but notinterground with the Portland cement particles and capable of reactingwith calcium hydroxide in the presence of water, including calciumhydroxide provided by the hydraulic cement particles when mixed withwater, in order to form solid hydration products having cementitiousproperties, the pozzolan fraction having a Blaine fineness, wherein theBlaine fineness of the Portland cement fraction is about 1.25 times toabout 50 times greater than the Blaine fineness of the pozzolanfraction, wherein a majority of the combined hydraulic cement andpozzolan particles above 20 μm are pozzolan particles and a majority ofthe combined hydraulic cement and pozzolan particles below 20 μm arehydraulic cement particles.
 32. A pozzolan cement composition as inclaim 31, wherein the Blaine fineness of the Portland cement fraction isgreater than about 500 m²/kg.
 33. A pozzolan cement composition as inclaim 31, wherein the Blaine fineness of the Portland cement fraction isgreater than about 650 m²/kg.
 34. A pozzolan cement composition as inclaim 31, wherein the Blaine fineness of the Portland cement fraction isgreater than about 800 m²/kg.
 35. A pozzolan cement composition as inclaim 31, wherein the pozzolan fraction comprises at least one of classF fly ash, class C fly ash, ground slag, or natural pozzolan.
 36. Apozzolan cement composition as in claim 31, further comprising water,fine aggregate, coarse aggregate and at least one of inert filler, lime,lye, water reducing admixture, accelerant, retardant, hydrationstabilizer, or rheology-modifying agent so as to form fresh concrete.37. A pozzolan cement composition as in claim 36, wherein the freshconcrete has a Vicat initial set time in a range of about 45-375 minutesand a maximum autoclave expansion of about 0.8%.
 38. A method ofmanufacturing the pozzolan cement composition of claim 31, comprising:obtaining the Portland cement fraction; obtaining the pozzolan fraction;and combining the Portland cement fraction and the pozzolan fraction toyield the pozzolan cement composition.
 39. A method as in claim 38,further comprising adding water to form a fresh cementitious compositionselected from the group consisting of concrete, mortar, grout, andmolding compositions.
 40. A method as in claim 39, wherein forming thefresh cementitious composition includes adding fine aggregate, coarseaggregate and at least one of inert filler, lime, lye, water reducingadmixture, accelerant, retardant, hydration stabilizer, orrheology-modifying agent to form fresh concrete.
 41. A method ofmanufacturing a pozzolan cement composition, comprising: obtaining ahydraulic cement fraction comprised of a distribution of differentlysized hydraulic cement particles at least partially comprised oftricalcium silicate and/or dicalcium silicate that provide excesscalcium hydroxide, when mixed with water, that is available for reactionwith a pozzolan, the hydraulic cement fraction having a Blaine finenessgreater than about 500 m²/kg and/or having a chemistry and a Blainefineness so that it qualifies as a Type III Portland cement under ASTMC-150; obtaining a pozzolan fraction that is initially separate from thehydraulic cement fraction and comprised of a distribution of differentlysized pozzolan particles capable of reacting with calcium hydroxide inthe presence of water in order to form solid hydration products havingcementitious properties, the pozzolan fraction having a Blaine finenessthat is less than the Blaine fineness of the hydraulic cement fraction,the Blaine fineness of the Portland cement fraction being about 1.25times to about 50 times greater than the Blaine fineness of the pozzolanfraction, a majority of the combined hydraulic cement and pozzolanparticles above 20 μm being pozzolan particles and a majority of thecombined hydraulic cement and pozzolan particles below 20 μm beinghydraulic cement particles; and combining the hydraulic cement fractionand the pozzolan fraction without intergrinding to yield the pozzolancement composition.
 42. A method as in claim 41, wherein the hydrauliccement fraction is combined with the pozzolan fraction in a manner so asto yield a dry blend of particles.
 43. A method as in claim 42, furthercomprising combining the dry blend of particles with water to form afresh cementitious composition selected from the group consisting ofconcrete, mortar, grout, and molding compositions.
 44. A method as inclaim 43, wherein forming the fresh cementitious composition includesadding fine aggregate, coarse aggregate and at least one of inertfiller, lime, lye, water reducing admixture, accelerant, retardant,hydration stabilizer, or rheology-modifying agent to form freshconcrete.
 45. A method as in claim 43, further comprising placing thefresh cementitious composition into a desired configuration and thenallowing it to harden.
 46. A method as in claim 41, wherein thehydraulic cement fraction is combined with the pozzolan fraction andwater in situ to yield a fresh cementitious composition selected fromthe group consisting of concrete, mortar, grout, and moldingcompositions.
 47. A method as in claim 46, wherein forming the freshcementitious composition includes adding fine aggregate, coarseaggregate and at least one of inert filler, lime, lye, water reducingadmixture, accelerant, retardant, hydration stabilizer, orrheology-modifying agent to form fresh concrete.
 48. A method as inclaim 47, further comprising placing the fresh concrete into a desiredconfiguration and then allowing it to harden.
 49. A method as in claim41, wherein the hydraulic cement fraction and the pozzolan fraction areblended together at a ready mix concrete plant.